In recent years, smaller computers with higher rate and higher capacity are realized, and UWB-IR (UltraWideband-Impulse Radio) attracts attention as a communication scheme that realizes high quality and high rate communication and that is capable of accommodating a large number of users.
The UWB-IR scheme utilizes the frequency band of several GHz using an impulse of 1 ns or less, and its occupied band width becomes ultrawideband. Therefore, the UWB-IR scheme uses frequency band including the band used in the existing system and may interfere with the existing system. However, the UWB-IR scheme has low signal power density characteristics and is not likely to interfere with other systems. Further, the UWB-IR scheme has wideband, and therefore is suitable for short-distance communication such as PAN (Personal Area Network).
On the other hand, there is an OFDM (Orthogonal Frequency Division Multiplex) scheme which has already been applied to a wireless LAN (Local Area Network) system and is most likely to be applied to the fourth generation mobile communication system, as commonly referred to. In the OFDM scheme, OFDM signals are generated by superimposing information signals and the like on a plurality of orthogonal carriers, and transmission signals are generated by performing predetermined transmission processing on the OFDM signals. The transmission signals are then amplified by a power amplifier and transmitted.
Therefore, the generated OFDM signals have a defect that peak power with respect to average power increases in proportion to the number of carriers. However, by appropriately suppressing the peak power, it is possible to amplify OFDM signals to large power at ease and realize wideband communication.
Patent Document 1 discloses a technique for preventing a wireless LAN system from causing and receiving interference upon use in the same area as or in a nearby area of the communication area of the UWB wireless transmission system. That is, by delaying an impulse signal by a time period corresponding to a reciprocal of use frequency of 5 GHz in the wireless LAN system and subtracting the delayed signal from the original signal, it is possible to attenuate the frequency signal used in the wireless LAN system and prevent interference.
Patent Document 1: Japanese Patent Application Laid-Open No. 2002-335188